Power hammers



H. H. HQFFMAN POWER HAMMERS July 26, 1966 5 Sheets-Sheet 1 Filed Aug. 17, 1965 R N CA W M Ew W0 H H T R E B R E H 26, 1966 H. H. HOFFMAN 3,262,506

POWER HAMMERS Filed Aug. 17', 1965 5 Sheets-Sheet 2 F/GZ INVENTOR HERBERT H. HOFFMAN July 26, 1966 H HOFFMAN 3,262,506

POWER HAMMERS Filed Aug. 17, 1965 5 Sheets-Sheet 5 United States Patent 3,262,506 POWER HAMMERS Herbert H. Hoffman, 39% Hazeltine Ava, Sherman Oaks, Calif. Filed Aug. 17, 1965, Ser. No. 482,034 6 Claims. (Cl. 173-98) This application is a continuation-in-part of my copending application Serial No. 382,998, filed July 14, 1964, entitled, Power Hammers, now abandoned.

This invention relates in general to power hammers used for impacting objects, such as in breaking up concrete or the like, and more particularly relates to an improvement in such power hammers whereby a rotating hammerhead impacts an anvil or tool holder in a novel, improved and more efficient manner.

Prior rotary hammers, as in Patent No. 2,500,402, have had the hammer heads mounted for radial movement while being rotated about a central axis so that the heads are free to rebound a limited amount on impacting an anvil or tool holder, However, in these radially movable rotating power hammer heads, the hammer heads have consisted of round or wheel-like members adapted to tangentially impact a round end of a tool holder. The impact thus effected occurred between a cylindrical surface on the wheel-like hammer head and a round tool end, being theoretically only a point contact. In practice, there would be elastic deformation of theimpacting hammer head and tool end which wastes energy. It is well known that the average force of a blow, such as between the hammer head and the tool end, is equal to the energy (ft. lbs.) divided by the penetration of either part into the other. Where a small impacting surface is provided as in the Patent No. 2,500,402, the penetration or elastic deformation of the impacting parts wastes energy and prevents the efficient transfer of energy from the hammer head into the tool holder.

It is a principal object of the present invention to disclose and provide a power hammer apparatus in which the rotating radially movable hammer heads impact an anvil or tool holder in a novel manner to very efficiently transfer energy from the hammer heads into the anvil or tool holder.

It is another object of the present invention to disclose and provide a power hammer apparatus as in the foregoing object wherein a maximum amount of surface contact is effected between the hammer head and anvil or tool holder during an impact blow by the hammer head on the anvil or tool holder.

It is another object of the present invention to disclose and provide a power hammer device having a housing providing a hammer chamber in which a transverse ro-' tatably mounted shaft rotatably mounts a yoke means for rotation within the chamber and wherein a pair of opposed unitary hammer heads are slidably mounted on the yoke to impact an anvil or tool holder projecting into the hammer chamber. It is a further object of the present invention to disclose and provide a power hammer device as in the foregoing object wherein each hammer head is provided with a tool impacting flat on an outer surface or edge of the hammer head and wherein the fiat is offset and inclined to the center line of the head radial movement on the yoke means to effect a maximum surface contact between the hammer head and the anvil or tool holder.

It is a still further object of the present invention to disclose and provide a power hammer device as in the foregoing objects wherein undesirable interferences between portions of the hammer heads and the anvil or tool holder prior to the desired impacts are eliminated and wherein all points of a specific zone or area defining a flat impact surface on the hammer head simultaneously impacts the anvil or tool holder.

These and other objects as well as various advantages of the power hammer of the present invention will be apparent to those skilled in the art from a consideration of the following detailed explanation of exemplary embodiments of the power hammer of the present invention. Reference will be made to the appended sheets of drawings in which:

FIG. 1 is a sectional view of an examplary embodiment of the power hammer according to the present invention.

FIG. 2 is a sectional view of the embodiment of FIG. 1 taken therein along the plane AA.

FIG. 3 is a detail view of a part of the embodiment of FIG. 1.

FIG. 4 is a schematic representation of a construction of the outer surfaces of the hammer head of the exemplary embodiment of power hammer according to the present invention.

FIG. 5 is a partial view of an embodiment of power hammer according to the present invention made with the hammer head configuration of FIG. 4 and shown prior to impact against an anvil or tool holder.

FIG. 6 is a partial view as in FIG. 5 showing the hammer head at the instant of impact with an anvil or tool holder.

FIG. 7 is a sectional view of the exemplary embodiment of FIGS. 4 through 6 showing the hammer head after impacting the anvil and tool holder.

Referring first to FIGS. 1 and 2, it may be seen that the exemplary power hammer includes a central ported housing member 1 and a pair of housing side plates 2 and 3. Central housing member 1 may be made from a solid piece of metal with a central hammer chamber 4, handle opening 5 and anvil bore 6 bored out or it may be cast. In th exemplary embodiment, the lower housing portion 7, central portion 8 and handle portion 9 are all made in one piece. The side plates 2 and 3 are fitted to the central portion 8 in recesses 9 and 10 to provide the central enclosed hammer chamber 4.

The hammer heads 11 and 12 are rotatably mounted within the hammer chamber 4 of housing 1 upon a onepiece yoke 13. Yoke 13 is fixed by key 14 to a shaft 15 which is centered within and extends transversely of the housing 1. The shaft 15 may be powered by any conventional means, such as by a flexible shaft interconnecting shaft 15 with a source of rotational power.

As best seen in FIG. 2, the transversely extending shaft 15 is rotatably mounted or journalled in a pair of spaced opposed bearings or journal members 16 and 17. The bearing members 16 and 17 are mounted, as by a tight press fit, to the coverplates 2 and 3 of the housing 1. The coverplates 2 and 3 may be bolted to the housing 1 by conventional bolt means 18 and 19,

The anvil bore 6 extends from the hammer chamber 4 down through the lower portion 7 of the housing 1. Bushing 20 is disposed in bore 6 to slidably receive an anvil and tool holder 21.

Anvil and tool holder member 21, as best seen in FIG. 2, is mounted to the housing by the bushings 6 and is limited in its sliding movement relative thereto by the set screw 22. Screw 22 operates on the anvil 21 through the elongated opening 23 provided in the anvil and tool holder member 21. A jam nut 24 may be provided for fixing the set screw 22 in its operative position as shown in FIG. 2.

The lower end of anvil and tool holder member 21 is provided with an outwardly extending flange 25. A plate 26 is slidably received on the anvil and tool holder 21 and is upwardly constrained thereon by the flange 25, as best seen in FIG. 2. As shown in FIG. 1, the plate 26 abuts a pair of compression springs 27 and 28 which are received and mounted in the lower portion 7 of the housing.

The compression springs 27 and 28 bias the anvil and tool holder 21 away from the hammer chamber 4, acting through the plate 26 abutting the flange 25 of the tool holder. These compression springs, therefore, serve to cushion the rebounding of the tool off of an object being worked on and serve to reduce the vibration from the tool into the housing and the handle portion 9.

Set screws 31, mounted to plate 26 by the jam nuts ,30, serve to limit the inward movement of the anvil and tool holder 21 relative to the housing 1. By adjusting the setting of the screws 31, the extent of projection of the anvil and tool holder 21 into the hammer chamber 4 of the housing may be controlled. By limiting the extent of inward travel of the tool holder into the hammer chamber, lighter impact blows may be imparted to the tool holder by the operation of the hammer heads as subsequently described.

The yoke 13 is provided with an elongated shaft-like :body portion with enlarged end flanges 33, as best seen in FIG. 1. Each of the hammer heads 11 and 12 is provided with an internal bore 34 and an inner enlarged bore area 35.

The axial extent of the chamber 35 within each hammer head is greater than the thickness of the end flange 33 of yoke 13 so that the hammer heads are allowed limited radial movement relative to the yoke 13.

On rotation of yoke 13, the hammer heads will move radially outward to a fully protracted or extended position as shown in FIG. 1 due to centrifugal force. On impacting the anvil and tool holder 21, inward radial rebounding of movement of the hammer heads is thus partially absorbed by the centrifugal force exerted on the hammer heads and is not directly transmitted to the yoke 13 and the housing 1.

The hammer heads 11 and 12 are retained upon the yoke 13 against lateral movement thereto by retainers 36 and 37 held together by cross bars 38.

As particularly contemplated within the present invention, each of the hammer heads 11 and 12 is provided with an anvil impacting zone thereon to transmit the rotational force of the hammer heads to the anvil and tool holder 21. The configuration of the hammer heads is of particular importance to the successful operation of the present hammer apparatus.

As seen in FIG. 1, each hammer head 11 and 12 is provided with an impacting zone 40 which is offset from the center line 41 of the yoke 13. Line 41 is also the center line of radial movement of the heads 11 and 12.

Impacting zone 40 is preferably made generally flat so that impacting forces will be transmitted over as wide a surf-ace contact with the tool holder and anvil 21 as possible. The upper end of tool holder 21 is provided with a generally fiat anvil-like surface 29 to be abutted by the generally flat impacting zone 40.

The flat or impact zone 40 is offset from the axis of head radial movement as shown in FIG. 1. The offset of flat 40 is to the left in FIG. 1 for the head 11 and to the right in FIG. 1 for head 12, in the direction of rotation of the heads in each case.

I have found that by making the impacting zone or [flat 40 inclined to the center line 41, or axis of head radial movement, at an angle 43 in FIG. 1 of about 15, a successful generally flat impact occurs between the zone 40 and anvil surface 29.

Further, to insure that the leading edge of the hammer head where the arcuate outer surface of the head joins the flat or zone 40, where the center line 41 intersects the outer surface of each head, does not prematurely impact and prevent a hat impacting of surface 40 on anvil 29, the arcuate portion of the head preceding the flat is cut away or reduced.

The preferred construction for the present hammer head configuration is illustrated in the schematic representation of FIG. 4. The outer circle having radius D represents the hammer cavity 4' of housing 1. The center A is therefore coincident with the center line or axis of the shaft 13 of FIG. 1. Point A is the center of rotation of the hammer heads represented by the arcuate members 11 and 12'.

Centers B and B represent the centers about which the initial outer curvature of the heads are drawn by the radii R and R At point G, where the vertical center line 41 representing the axis of radial movement of the heads, intersects the arc of radius R an impacting zone or flat F is constructed at an incline of 15 to the horizontal or, with a included angle with the vertical center line 41.

At this stage in the construction, a flat has been provided in the arcuate outer surface of the head, the outer surface or are of the head being defined by swinging r-adius R through at least In order to reduce the portions of the head preceding the flat to avoid interference between the head and the anvil prior to impacting between the flat and anvil as desired, a new surface contour for the portion of the head preceding the fiat is provided.

The movement of the flat or zone F within the housing is about the head center of rotation, point A. Therefore, radius H is drawn from the center of rotation A to point E along flat F so that H is the shortest distance between the flat F and the center of rotation A. An are I is then drawn by swinging the radius H about the center of rotation A until it intersects the original outer surface of the head at about point K.

The new outer configuration of the hammer head 11 is thus formed by the radius of curvature R flat F and the arcuate portion I. The arcuate portion J preceding the fiat F has a larger radius of curvature H than the head radius of curvature R for the arcuate portion L following flat P In operation, as shown in FIG. 5, the radially extended hammer head 11' first contacts the anvil or tool holder 21 along the first arcuate portion J of the head preceding the impacting zone or flat F No impact is caused at this time.

As shown in FIG. 6, the flat or impact zone F, then comes into contact with the anvil surface 29 of the tool 21 causing impact. The rebound of the head 11 and ejection of tool holder 21 out of the hammer chamber against the associated tool is shown in FIG. 7.

The foregoing description and examples are only illustrative of the present invention and should not be considered as limitations of its scope. Other modifications, alterations and variations of the present invention may be made by persons skilled in the art which come within the scope of the present invention, which is defined and limited only by the following claims.

I claim:

1. In a power hammer device having a housing providing a hammer chamber, a transverse rotatably mounted shaft extending through said chamber and a tool holder, including means for slidably mounting the tool holder relative to the housing, extending partly into said hammer chamber to be impacted by a hammer within the chamber, the provision of:

yoke means mounted on said shaft to be rotated by said shaft Within said hammer chamber;

a pair of opposed hammer heads, each said head comprising a unitary mass slidably mounted on said yoke means for limited radial movement and having an arcuate outer edge;

a tool holder impacting flat provided in said outer edge of each said hammer head, each said flat being offset from and inclined to a centerline of head radial movement relative to said yoke means; and

an arcuate portion in said outer edge of each head preceding the associated flat in the direction of head rotation which has a larger radius of curvature than arcuate portions of said edge following said associated flat.

2. The provision in a power hammer device of claim 1 wherein: 7

each said flat is oriented on the outer edge of its associated hammer head so that it forms a chord of an angle 'whose apex intersects said cente-rline.

3. The provision in a power hammer device of claim 2 wherein:

each said flat is offset from the centerline of head radial movement in the direction of head rotation.

4. In a power hammer device having at least one hammer head rotatable about and radially movable relative to a central axis anda tool holder slidably mounted for movement normal to said axis and having an anvil surface to be impacted by the rotating hammer head, the provision of:

a generally flat anvil impacting zone on an outer surface of the hammer head to impact against the tool holder anvil surface on rotation of the head, said impacting zone being offset of a centerline of head radial movement in the direction of head rotation, and

means for providing a reduced portion on each hammer head preceding the generally flat anvil impacting zone for preventing interference between the hammer head outer surtace and the anvil surface prior to impacting between the hammer head anvil impacting zone and the anvil surface.

5. In an impact hammer apparatus having a housing containing at least one hammer head rotatable about a central shaft to impact an anvil portion of a tool holder extending into the housing, the provision of:

yoke means mounted to the central shaft for rotation within the housing including a body portion and an outwardly extending end flange portion;

a unitary hammer head having an arcuate outer surface, a central bore slidably receiving the yoke means body portion and an internal enlarged bore portion inwardly of said central bore receiving the yoke means end flange portion, said enlarged bore portion being of greater axial extent than said end flange portion to allow limited radial movement of said head on said yoke means;

an anvil impacting zone on said hammer head, said zone comprising a generally flat sur face formed in the arcuate outer surface of the head inclined to a centerline of head radial movement and oflfset therefrom in the direction of head rotation; and

a first arouate portion of said head outer surface preceding said impacting zone in the direction of head rotation having a larger radius of curvature than a second arcuate portion of said head outer surface following said impacting zone.

6. In a power hammer apparatus having a housing and a tool holder slidably mounted thereto for impacting by a hammer rotatable within the housing, the provision of:

a pair of one piece hammer heads mounted to a one piece yoke for limited radial movement relative to the yoke;

means for rotatably mounting the yoke to bring said heads into engagement with said tool holder on rotation of the yoke,

offset flat means on each said hammer head to abut said tool holder on said engagement; and

reduced portions on each said hammer head preceding said flat means to prevent interference between said head and tool holder prior to said engagement.

References Cited by the Examiner UNITED STATES PATENTS 1,399,387 12/ 1921 Jackson 17394 1,531,549 3/ 1925 Georgevich 173-98 2,500,402 3/1950 Craig 173-94 MILTON KAUFMAN, Primary Examiner. 

1. IN A POWER HAMMER DEVICE HAVING A HOUSING PROVIDING A HAMMER CHAMBER, A TRANSVERSE ROTATABLY MOUNTED SHAFT EXTENDING THROUGH SAID CHAMBER AND A TOOL HOLDER, INCLUDING MEANS FOR SLIDABLY MOUNTING THE TOOL HOLDER RELATIVE TO THE HOUSING, EXTENDING PARTLY INTO SAID HAMMER CHAMBER TO BE IMPACTED BY A HAMMER WITHIN THE CHAMBER, THE PROVISION OF: YOKE MEANS MOUNTED ON SAID SHAFT TO BE ROTATED BY SAID SHAFT WITHIN SAID HAMMER CHAMBER; A PAIR OF OPPOSED HAMMER HEADS, EACH SAID HEAD COMPRISING A UNITARY MASS SLIDABLY MOUNTED ON SAID YOKE MEANS FOR LIMITED RADIAL MOVEMENT AND HAVING AN ARCUATE OUTER EDGE; A TOOL HOLDER IMPACTING FLAT PROVIDED IN SAID OUTER EDGE OF EACH SAID HAMMER HEAD, EACH SAID FLAT BEING OFFSET FROM AND INCLINED TO A CENTERLINE OF HEAD RADIAL MOVEMENT RELATIVE TO SAID YOKE MEANS; AND 